More than 20 years after the introductionof oral contraceptives in the United States, it seems that -- with the possible exception of one subgroup of women -- the pill has not increased women's risk of breast cancer.

The findings come from the largeststudy to date on the subject, released in the Aug. 14 NEW ENGLAND JOURNAL OF MEDICINE. Caveats and questions remain, but, says an accompanying editorial, the study as a whole should reassure physicians and pill users.

Because there is a great deal of evidencethat hormones play a part in causing breast cancer, the use of oral contraceptives, which are based on hormones, has long been a matter of concern. Hormone-related factors such as age at first menstruation or first full-term pregnancy, for instance, can affect a woman's risk of breast cancer throughout her lifetime.

Though most investigations havegiven the pill good grades regarding breast cancer, some have raised questions about subgroups of women who might be at particular risk -- women who use certain types of birth control pills, or women who hae used the pill before their first full-term pregnancy (SN: 11/9/85, p. 293). But the studies were too small to provide definitive answers; and because most were conducted in the early 1970s, they could not analyze the pill's long-term effects. The new study took up those questions.

"For the time," says Richard Sattinof the Centers for Disease Control (CDC) in Atlanta, who led a large team of investigators, "we had enough numbers so that we could look at subgroups of women and patterns of [birth control pill] use." The study, conducted by the CDC and the National Institute of Child Health and Human Development in Bethesda, Md., compared the oral contraceptive use of 4,711 women with newly diagnosed breast cancer with that of 4,676 controls.

Use of the Pill for 15 or more years hadno effect on a woman's risk of developing breast cancer, according to the researchers; nor did it matter how long it had been since the last use of the pill. Neither a family history of breast cancer nor a personal history of benign breast disease made women more vulnerable to pill-related breast cancer; nor did use of the pill before a full-term pregnancy. And there was no evidence that use of any particular type of pill increased the risk of breast cancer.

There is concern that those womenwho use oral contraceptives when they are very young (mid-teens), while theire breasts are developing rapidly, may be more vulnerable to breast cancer. But since few women in that age group took the pill when it was first introduced in the early 1960s, Sattin says, the study couldn't draw any conclusions about the long-term effects of such use. "The evidence for young women will still take quite a while," Sattin says. "There's a lot of conflicting evidence about that."

Indeed, the very long-term effects ofpill use by women of any age may not be known for another decade. Samuel Shapiro of the Boston University School of Medicine points out in an accompanying editorial that there are no data on what happens more than 15 years after women stop taking the pill. And as women begin to pass that mark, he adds, they will also be entering the age range in which the incidence of breast cancer climbs steeply.

Other questions that remain open includethe effects of new formulations of birth control pills and the effects of patterns of pill use outside the United States. Shapiro adds that the study addresses only the question of breast cancer, and not other possible side effects of the pill, which include an increased risk of heart attack. However, he writes, "From a public health viewpoint, as best we can judge on the present evidence, that cost [of oral contraceptives] is acceptable, at least in the United States."

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